S. S. Ermakov

Vapor permeation-stepwise injection simultaneous determination of methanol and ethanol in biodiesel with voltammetric detection.

A novel vapor permeation-stepwise injection (VP-SWI) method for the determination of methanol and ethanol in biodiesel samples is discussed. In the current study, stepwise injection analysis was successfully combined with voltammetric detection and vapor permeation. This method is based on the separation of methanol and ethanol from a sample using a vapor permeation module (VPM) with a selective polymer membrane based on poly(phenylene isophtalamide) (PA) containing high amounts of a residual solvent. After the evaporation into the headspace of the VPM, methanol and ethanol were transported, by gas bubbling, through a PA membrane to a mixing chamber equipped with a voltammetric detector. Ethanol was selectively detected at +0.19 V, and both compounds were detected at +1.20 V. Current subtractions (using a correction factor) were used for the selective determination of methanol. A linear range between 0.05 and 0.5% (m/m) was established for each analyte. The limits of detection were estimated at 0.02% (m/m) for ethanol and methanol. The sample throughput was 5 samples h(-1). The method was successfully applied to the analysis of biodiesel samples.

Electrochemical polishing of the surface of a gold electrode and its effect on the sensitivity of the stripping voltammetric determination of mercury(II)

The effect of two different techniques for the preparation of the surface of a gold electrode on the sensitivity of the stripping voltammetric determination of mercury(II) was studied. The electrochemical polishing of the electrode in a solution containing thiourea, sulfuric acid, and ammonium thiocyanate lowered the detection limit for mercury down to 2 ng/L and improved the reproducibility of mercury anodic peaks.

Non-enzymatic sensors based on in situ laser-induced synthesis of copper-gold and gold nano-sized microstructures

The synthesis of conductive gold and copper-gold microstructures with high developed surface based on the method of laser-induced metal deposition from solution was developed. The topology and crystallization phase of these structures were observed by means of scanning electron microscopy and X-ray diffraction, respectively. The electrochemical properties of the synthesized materials were investigated using cyclic voltamperometry and amperometry. According to the obtained results, it was found out that copper-gold microstructures demonstrate a linear dependence of Faraday current vs. concentration from 0.025 to 5µM for D-glucose and from 0.025 to 10µM for hydrogen peroxide. In turn, gold deposit exhibits a linear dependence of Faraday current vs. concentration from 0.025 to 50µM for D-glucose and from 0.025 to 1µM for hydrogen peroxide. Moreover, the synthesized materials reveal low detection limits (0.025µM) with respect to the aforementioned analytes, which is quite promising for their potential application in design and fabrication of new non-enzymatic biosensors.

Nonenzymatic determination of glucose on electrodes prepared by directed electrochemical nanowire assembly (DENA)

The analytical characteristics of gold nanowires prepared by direct electrochemical synthesis were studied with the use of the amperometric determination of glucose as an example. The applicability of the gold nanowires to the determination of glucose in a neutral medium (a phosphate buffer solution with pH 7.2) over a concentration range from 1 × 10–4 to 5 × 10–3 M at a detection potential of +0.35 V was shown. It was found that the sensitivity of a nonenzymatic sensor for the determination of glucose on the gold nanowires was high: 3.7 × 10–4 A M–1 m–2. The limit of detection was 3.3 × 10–5 M.

Determination of mercury in air by stripping voltammetry with chromatomembrane preconcentration

It is shown that mercury can be determined in air by stripping voltammetry at a level of 0.05 μg/m3 (0.005 MPC in the air of working areas) using chromatomembrane preconcentration.

Use of a coulometric sensor for automation of the oxygen concentration measurements in process waters of thermal power plants

A coulometric procedure was suggested for determining the concentration of dissolved oxygen in water. The procedure can be used for automation of measurements at nuclear and thermal power plants. The sensor design was developed for experimental check of the procedure, and operation parameters of the sensor were found. The concentrations calculated from the results of coulometric measurements are in good agreement with those found amperometrically with the classical Clark sensor.

A rapid version of standardless stripping voltammetry for determining mercury in aqueous solutions

It was shown that mercury(II) in aqueous solutions can be determined by standardless stripping voltammetry based on the determination of the coulometric constant of the electrochemical cell. This approach considerably reduces the analysis time in comparison to the known analogs. The coulometric constants were found for electrochemical cells with a gold and a gold-graphite film electrodes in solutions of different volumes. The optimum time of preelectrolysis was determined for measurements using the proposed method.

Interrupted amperometry on solid electrodes: Determination of hydroquinone and phenol

The new method, interrupted amperometry, is proposed to increase the sensitivity of amperometric measurements. Analytical possibilities of interrupted amperometry on solid electrodes are studied on an example of the determination of phenolic compounds in aqueous solutions.

A combined standardless electrochemical method for determining lead in aqueous solutions

A combined standardless method for determining lead(II) in aqueous solutions is proposed. The method is based on lows stripping voltammetry and controlled-potential coulometry.

Combined standardless electrochemical method for determination of lead(II), copper(II), and cadmium(II) in aqueous solutions

A combined standardless method (no calibration of the device against standard solutions or use of the method of additives is required) for determination of lead, copper, and cadmium in aqueous solutions is suggested. The method operates on principles of inversion voltammetry and potentiostatic coulometry. It is convenient for automated analysis of technological solutions and wastewater from electroplating and hydrometallurgical shops.